Brown — Note on the Decay of Magnetism in Bar Magnets. 79' 



Table I. 



A = Magnetic moment per gramme in December, 1909, or six montlis after being magnetized. 

 jB = Percentage loss in magnetic moment six montlis after being magnetized. 

 C = Magnetic moment per gramme in January, 1920. 



D = Percentage loss in magnetic moment for a period of about ten years, or from December, 

 1909, till January, 1920. 



It will be seen from the table that No. 2 magnet has lost very little of its 

 magnetism after the first six montlis, and seems to have settled down to a 

 practically permanent state. The fairly high carbon and manganese makes 

 this a good permanent magnet, though its actual moment is not very high. 



Comparing Nos. 3 and 4, which have the same amount of manganese and 

 fairly high carbon, the latter, having also 1 per cent, of nickel, has four times 

 the retentivity of the former, though the percentage loss in the six months 

 after being magnetized is nearly double of that in No. 3. Taking Nos. 2 and 14, 

 which have the same amount of carbon, and the latter a high percentage of 

 chromium, the presence of the chromium has reduced the retentivity ten 

 times, which confirms a result given by the writer in another paper, namely, 

 that more than about 2-5 per cent, of chromium in steel decieases its value as 

 a magnet.^ 



1 Solent. Proc. Roy. Dub. Soc, April, 1910, vol. xii, pp. 349-353. 



SCIENT. PROC. R.D.S., VOL. XVI, KG. VI. K 



MAR" 5 ^s921 



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